The present invention pertains to communication system failures and more particularly to automatic protection switching in such communication systems.
Communication system traffic is routed to a central point to perform the data transfer and switching functions. This central point is a mobile switching center. The mobile switching center is typically coupled to a digital cross connect switch on E1 or T1 links. The digital cross connect switch aggregates multiple T1/E1 interfaces to the optical SONET/SDH interfaces terminating at the network element. These features may be embedded into a single product which is sold by mobile switching system manufacturers.
Typically line equipment is coupled to the digital cross connect switch via OC3 links. These OC3 links may run considerable distances, for example.
All too frequently, these lines or fiber connections are severed by backhoes or other digging equipment and are covered by automatic protection switching standards. Automatic protection switching standards have been implemented into communication systems in order to alleviate the problems with failures due to lines being severed. Today's competitive markets demand that communication systems provide near continuous functionality. Therefore it is imperative that 99.999 percent of the time that the communication system smoothly handle data transmission.
Automatic protection switching typically uses two OC3 fibers to couple a particular piece of line equipment to a digital cross connect switch or to the mobile switching center in either a 1+1 or 1:N redundancy mode. In that manner if one of the links or cables is severed, the other one may survive and be able to provide full services for data transmission seamlessly. However, a digging accident may sever both OC3 links providing the working and protection services for a particular piece of line equipment. In addition, the line termination equipment itself may fail.
Accordingly, it would be highly desirable to have an arrangement to provide a seamless protection arrangement for faults due to OC3 cabling as well as protection for line termination equipment failure.